Acrylic resins have excellent transparency and can be easily processed, and are therefore widely used as films, sheets, or general molded articles.
Particularly, acrylic resins having a glutaric anhydride structure or a glutarimide structural unit have excellent transparency and heat resistance and a small photoelastic constant, and therefore their use as optical materials has been studied. For example, Patent Document 1 discloses an optical film composed of a glutarimide acrylic resin. Patent Document 2 discloses a phase difference film composed of a glutarimide acrylic resin. However, a glutarimide acrylic resin generally has a problem that its mechanical strength is not always sufficient.
Various studies have been made to improve the mechanical strength of a glutarimide acrylic resin. Particularly, impact resistance is preferably improved using an impact resistance-improving agent of a type called “core-shell type”, which is obtained by graft polymerization of a vinyl-based monomer onto a rubbery polymer. Specific examples of the rubbery polymer include butadiene-based rubber, acrylic rubber, and polyorganosiloxane-based rubber. However, addition of butadiene-based rubber causes a problem that the weather resistance of the resin is significantly impaired. Patent Document 3 discloses that polyorganosiloxane-based rubber is added to improve impact resistance, but this causes a problem that a resulting resin has impaired transparency.
Patent Document 4 states that a resin composition having excellent heat resistance and mechanical strength (especially, bending resistance) can be obtained by mixing a glutarimide acrylic resin and an acrylic graft copolymer.